The present invention relates to polytrimethylene terephthalate (hereinafter referred to as PTT) monofilament yarn, a method for producing the same, and brushes using the monofilament yarn.
In the prior art, monofilaments prepared from thermoplastic resins such as nylon or others have been widely used as raw material for bristles of tooth brushes, cosmetic brushes, hair brushes or various industrial brushes. For example, nylon 612 has been often used as bristles of tooth brushes because it is soft in touch during use to hardly hurt teeth or gums and has a relatively favorable elastic recovery. Nylon, however, is high in moisture absorption and if it absorbs moisture, physical properties and elastic recovery thereof are lowered and the dimension thereof largely changes, whereby there is a problem in that if the brushes are continuously used for a long time, bristles are opened from each other to lower the durability. Also, there is another problem in that the material cost is expensive.
A PTT fiber has been known for a long time, and a multifilament yarn for clothing is disclosed in Japanese Unexamined Patent Publication No. 52-5320 or 58-104216. Also, PTT monofilament yarns are described in (A) Japanese Unexamined Patent Publication No. 5-262862, (B) No. 8-120521 or (C) No. 11-48631, and tooth brushes using the PTT monofilament yarn are disclosed in (D) Japanese Unexamined Publication No. 8-173244 or (E) a published pamphlet WO99/05936.
In the above document (A), a PTT monofilament yarn suitable for a gut of a tennis racket is described, and in Example 5 thereof, the PTT monofilament yarn for a tennis racket gut having an intrinsic viscosity of 1.05 dl/g and a fiber size of 657 denier (730 dtex) is disclosed.
In the document (B), a PTT monofilament yarn suitable for a paper-making canvas is disclosed. It is described in the document (B) that the PTT monofilament yarn disclosed in the document (B) is characterized by a low concentration of terminal carboxyl groups whereby it is high in resistance to hydrolysis (resistance to wet heat). In Example 1, a PTT monofilament yarn is described, having an intrinsic viscosity of 0.95 dl/g and a diameter of 0.4 mm (a fiber size of 1716 dtex).
In the document (C), a gauze for a printing screen using PTT monofilament yarns is disclosed. It is described in the document (C) that the PTT monofilament yarn of a gauze for a printing screen preferably has a fiber size in a range from 8 to 55 dtex (from 7 to 50 denier). In Example 1 thereof, a PTT monofilament yarn is described, having an intrinsic viscosity of 0.89 dl/g, a fiber size of 17 dtex and an elongation at break of 45%.
However, there is neither description nor suggestion in any of the documents (A), (B) and (C) regarding the suitability of the PTT monofilament yarn for brush bristles.
The documents (D) and (E) disclose a brush using PTT monofilament yarn. In an Example of the document (E), the PTT monofilament yarn suitable for tooth brush is described, having a diameter of 0.175 mm (a fiber size of approximately 325 dtex) and a diameter of 0.208 mm (a fiber size of approximately 460 dtex). According to the present inventors, however, it was found that a tooth brush satisfactory in bending recovery and a dimensional stability is not obtainable by the mere application of the PTT monofilament yarn.
In the document (D), there is a description in that an intrinsic viscosity of the PTT monofilament yarn is preferably 0.5 dl/g or more, and in Example 1 thereof, a tooth brush is described which is obtained by filling a PTT monofilament yarn having a diameter of 0.22 mm (a fiber size of approximately 515 dtex) produced from PTT resin having an intrinsic viscosity of 0.70 dl/g, which is spun, cooled and heat-drawn, and thereafter subjected to a constant-length heat set at 140xc2x0 C. for 10 minutes. As the PTT monofilament yarn obtained under such conditions is low in intrinsic viscosity (in other words, low in degree of polymerization), it is also low in toughness and in elastic recovery. Therefore, when used as a brush bristle, splits, wear or opening due to the fatigue of bristle might occur within a short period.
Also, according to Example described in the document (D), the residual heat shrinkage is high because of unsuitable heat-setting conditions after the drawing process. Thereby, during a filling process for tooth brushes, the standing upright (the straightening) of the brush bristles becomes worse due to heat generated when the bristles are trimmed (to align tips thereof) or end-rounded (to round tips thereof), resulting in the bend of bristles or the opening of bristles. Further, due to the heat treatment after the brush has been completed, such as a high-temperature sterilizing treatment, deformation, kink or opening of the bristle may occur, whereby this yarn is unsatisfactory as brush bristles.
An object of the present invention is to provide a monofilament yarn excellent in softness, bending recovery or durability against a long term use, and a method for producing the same.
That is, the present invention is as follows:
1. A PTT monofilament yarn constituted by PTT composed of 90 mol % or more of trimethylene terephthalate repeating units and 10 mol % or less of other ester repeating units, wherein the yarn has a single-fiber size of 50 dtex or more, an intrinsic viscosity in a range from 0.8 to 1.3 dl/g, and a boiling water shrinkage of 2% or less.
2. A PTT monofilament yarn as defined by the above item 1, wherein the boiling water shrinkage is in a range from 0 to 1.5%.
3. A PTT monofilament yarn as defined by the above item 1 or 2, wherein a peak temperature of a mechanical loss tangent is in a range from 100 to 120xc2x0 C.
4. A PTT monofilament yarn as defined by any one of the above items 1 to 3, wherein the yarn contains particles, in a range from 0.01 to 5 wt %, which have an average diameter in a range from 0.01 to 5 xcexcm
5. A brush filled with bristles of the PTT monofilament yarn defined by any one of the above items 1 to 4.
6. A method for producing a PTT monofilament yarn, wherein after a raw material PTT monofilament yarn having a fiber size of 50 dtex or more is spun and drawn, the raw material PTT monofilament yarn is subjected to a relaxation heat treatment under the condition of a relaxation ratio in a range from xe2x88x9210 to +15% and a heat treatment temperature in a range from 100 to 180xc2x0 C.
7. A method for producing a PTT monofilament yarn as defined by the above item 6, wherein the relaxation ratio is in a range from 1 to 15%.